Although he was born in a small rural community west of Hamilton, Ontario, Reginald "Red" Horner was playing bantam hockey with North Toronto by his early teens. He was one of seventy-two players trying out for Frank Selke's Marlboro juniors in 1926 and although young "Red" did not distinguish himself in that first practice, Selke felt that he would be as patient as possible with Horner. The fact that Red was Selke's grocery boy didn't hurt his chances but Horner nonetheless made the squad on his own merits. "He has his elbow in your kisser or his fanny in your face every time he is on the ice," said Marlie captain "Shrimp" MacPherson.

Conn Smythe thought that Horner's robust style was being wasted in the amateur leagues and soon called Red up to the Maple Leafs. Horner had already played a Friday night game with the Marlboro juniors and a Saturday afternoon tilt in the brokers' senior league when he was informed of his new assignment for Saturday night at the Gardens. He made his National Hockey League debut on December 22, 1928, at home against the Pittsburgh Pirates. The game was Horner's third in a span of twenty-four hours. He suffered a broken hand in his second game and missed a good portion of the season, finishing his rookie campaign without any points and 30 penalty minutes in the 22 games he played. The statistical imbalance of points to penalty minutes would become a consistency in Horner's career.

He was not a graceful skater but could move the puck up ice quickly, usually feeding a tape-to-tape pass while having two forecheckers bearing down on him. Horner's tough, physical style of play earned him the league leadership in penalty minutes for eight of his twelve NHL seasons. He played in the 1934 and 1937 Benefit games for Ace Bailey and Howie Mrenz and was on a Cup winner with Toronto in 1932.

He played in a day when goaltenders served their own penalties and himself was called upon twice in his career to defend the Toronto net, surrendering one goal in three minutes of play, while his goalie sat in the penalty box. Horner played his entire career with the Maple Leafs and served as team captain from 1938 until his retirement in 1940.

Now into his nineties, he resides in Toronto but spends some of his time in Florida during the winter. He is the oldest living Maple Leaf captain and oldest living member of the Hockey Hall of Fame and was involved in the opening ceremonies for both the 65th anniversary of Maple Leaf Gardens and the closing of the Gardens on February 13, 1999.